Zinsco Panel -- Almost Missed A Defect (Mini Question of the Week without a prize?)

[dhorton2 (Daniel Horton, CMI®)]

@bnesbitt

The ground path is from the center screw on a 2-prong outlet, or the 3rd prong, via the frame of the device to the box. From the box to the dedicated 16 gauge wire to the frame of the subpanel. At

Yes, I understand how a self grounding receptacle works, that’s why I mentioned it.
Your pic shows a 16 g grounding conductor coming out of the box and ending at the flange of the box. (And no egc in the form of conduit)
And If the circuit grounds are not connected at the panel, then there is no path back to the sub panel

[rmeier2 (Robert Meier)]

@bnesbitt

Frist it certainly was professionally done and correct at the time. No code upgrade is required in the USA for legally done past work. The workmanship is not an issue.

That’s correct, around here many homes built in the 50’s and 60’s were using the same method for the EGC. Around here they did connect to the box. This one had a ground screw on the outside of the box which was removed.

[bnesbitt (Bryce Nesbitt)]

@dhorton2

Your pic shows a 16 g grounding conductor coming out of the box and ending at the flange of the box. (And no egc in the form of conduit)

Ah, I see the understanding gap.
My intent in showing the picture was educational.

The NM cable of the day had a third wire, which was wrapped back up out of the box, and clamped on the outside. Thus it appears at first glance there’s no separate ground wire, but it’s actually there.

And frankly that method avoids a risk with the modern method. How many times have you seen scorching because the bare ground wire got tangled up inside the box with the current carrying conductors. Eh? Can’t happen with the 1960’s system.